1. Technical Field of the Disclosure
The present invention is related in general to the field of drive units and, more particularly, to irrigation drive units that can detect a change in stress and can turn the wheels of the irrigation systems to eliminate the stress.
2. Description of the Related Art
Conventional irrigation systems include a corner pivot irrigation system, a center pivot irrigation system or a linear move irrigation system. These irrigation systems include a series of interconnected irrigator spans having conduits for conveying fluid to an agricultural field. Such irrigation systems typically include a water delivery pipeline which is supported by a plurality of structural steel towers or drive units. The steel towers or drive units provide support to the main water supply pipe above the ground, and are driven at slow speeds to move the tower or drive unit in a circular path about the central pivot, or in a linear path in the case of linear move systems, over the field to be irrigated. Each of the steel towers or drive units has spaced apart drive wheels which are driven by any convenient means such as an electric motor which is connected to a gearbox at each end of the main beam of the towers or drive units. The towers or drive units usually have at least two wheel/tire assemblies associated therewith which contact the ground and support a substantial percentage of the total weight of the system. However conventional irrigation systems have considerable drawbacks. In such irrigation systems, the drive wheels can only move in a straight forward alignment. Drive wheels which are aligned in a straight forward configuration can cause a change of arching on a truss span resulting in increased stress on the pipeline.
For example, a drive unit for a self-propelled irrigation system may include an elongated pipeline supported upon a plurality of spaced-apart drive units. A first drive assembly and a second drive assembly may be pivotally connected to a base beam having a first end and a second end thereof. Each of the first and the second drive assemblies may include an elongated support member pivotally connected, about a generally vertical axis, which is generally transverse to the longitudinal axis of the base beam, to the base beam adjacent the first end thereof. First and second driven wheels may be rotatably mounted on the elongated support member adjacent the ends thereof. The drive wheels are driven by an electric motor and gearbox arrangement. However, the drive unit is cumbersome and creates arching or pulling on the truss span due to the heavy load as the drive wheels move through the field. The drive unit cannot detect a change in the stress on the span and is unable to provide proper alignment of the drive wheels to eliminate the stress on the span.
Another existing system discloses an irrigation system with a corner irrigator span comprising a main irrigation portion having an end irrigator span. A control system controls the movement of the corner irrigator span. The control system includes a linear movement control system to control a corner drive unit of the corner irrigator span and a steering control system that controls a steering unit of the corner irrigator span. A disadvantage of this system is that the steering control system only provides steering to the corner irrigator span but does not allow turning of the drive wheels. In this system the drive wheels are arranged in a straight forward alignment that allows only linear movement of the drive wheels.
Recent advancements in the art provide a self-propelled irrigation machine including an elongated main boom pivoted at one end to a center pivot and supported on a plurality of self-propelled, non-steerable drive towers. An extension boom is pivotally secured to the other end of the main boom for irrigating corner areas of the field. A steerable drive tower supports the extension boom and includes a pair of steerable drive wheels. The guidance and control for the extension boom utilizes GPS receivers as position sensors. The system is comprised of two GPS units, two microprocessor-based smart boxes, a communications link running from the pivot to the steerable drive unit, and an angle sensor to monitor the angle of the corner arm steerable wheels. However, the system has a complex structure and the GPS units and communications link running from the pivot to the steerable drive unit may be subject to error based on the inconsistent motion of the drive wheels to which they are attached. This error and inconsistent motion causes crowning or arching of the span of the irrigation system.
Based on the foregoing, there is a need for a drive unit which would allow steering of the drive wheels to allow specific circular or linear movement of the drive wheels. Such a needed system would detect a change in the stress on the span and provide proper alignment of the drive wheel to eliminate the stress. Such a needed system would reduce the effect of load on the system and reduce metal and system fatigue from the load on the system. Such a needed system would be simple in construction and would also be steered to realign spans for storage configuration in a field and to provide specific irrigation patterns. The present invention overcomes prior art shortcomings by accomplishing these critical objectives.